Water heating and/or space heating appliances use heat created by a burner in a combustion chamber and transfer this heat to a fluid to be heated. Systems for accomplishing this task are described in U.S. Pat. No. 5,022,352 and U.S. Pat. No. 4,766,883 referred to above. These patents describe the workings of the burner and mechanical elements supporting the burner which create heat in the combustion chamber. The combustion chamber is surrounded by a body of water, which is contained within a closed tank which is in turn surrounded by a body of insulation. The products of combustion created in the combustion chamber exit the combustion chamber and pass through a helical tube of several turns within the body of water. The heat of combustion warms the walls of the combustion chamber and the helical tube. This heat is transferred to the water contained within the surrounding tank. The heated water from the water heater may also be used to heat the air of a home or building by piping the hot water to a heat exchanger designed for that purpose. The systems described in both U.S. Pat. Nos. 4,766,883 and 5,022,352 use a metallic water containing tank. Use of metallic tanks is conventional in water heaters. The tank is normally constructed of several pieces, including a cylindrical side wall, a top and a bottom. Holes are cut into the tank where access is required and fittings welded into the tank so that hot water outlet tubes, cold water inlet tubes, thermostats and the like can be accommodated and the access points sealed.
Such metallic tank structures have posed numerous problems in the past. If conventional steel is used, a coating must be applied to the interior of the tank to prevent corrosion. Where welds, fittings and joints are present, maintenance of integrity of an interior coating is difficult. Breaks or blemishes in the interior coating allow corrosion, which further compromises the coating and can lead to failure of the tank. One means of addressing this problem is the use of stainless steel; however, stainless steel is very expensive. Moreover, stainless steel must still be welded to provide fittings for the admission of inlets, outlets and sensors. The chemistry of weld metal is not always precisely controllable and corrosion susceptible areas can result. Corrosion resulting in a leak in a stainless steel tank, even if minuscule, normally results in total loss of the appliance. The leak is usually not discovered until it has allowed leaking fluid to destroy other elements of the structure.
It must be remembered that water heaters are mass produced products for sale in an extremely price competitive marketplace. A solution to a problem is not a real solution unless it can be implemented in a production line for large quantities of products. Moreover, it must be capable of uniform application in a mass production facility. The present inventions contemplates a new and improved tank structure which overcomes the above-referred to problems and others and provides a water heater of high efficiency, reliability, stability and quality. Moreover, the present invention provides a method of manufacturing such water heaters particularly useful in the mass production of commercial products.